Cellular membranes contain several classes of glycerophospholipids, which have numerous structural and functional roles in cells. Membrane diversity and asymmetry are important for membrane fluidity, curvature, and storage of lipid mediator precursors. Using acyl-CoAs, glycerophospholipids are first formed in the de novo pathway (Kennedy pathway), and then modified in the remodeling pathway (Lands' cycle) to generate mature membrane. Recently, several lysophospholipid acyltransferases (LPL-ATs) from two families, the 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) family and the membrane bound O-acyltransferase (MBOAT) family, were shown to function in the remodeling pathway. The MBOAT family possesses either LPLAT activity or protein O-acyltransferase activity. While the motifs of the AGPAT family have been well characterized, the MBOAT motifs remain unclear. In this study, we identified four MBOAT motifs essential for LPLAT activities by extensive site-directed mutagenesis. These findings further Our understanding of the enzyme reaction mechanisms and will contribute to structure predictions for the MBOAT family enzymes. (C) 2009 Elsevier Inc. All rights reserved.